Water Hammer After Mixing Valve

[Raymond1972]

Hi. I am stumped on how to fix this water hammer issue.

Redoing our bathroom and we put the mixing valve on one wall and shower head on another wall. There is no tub. I ran the shower line from the mixing valve down into the basement, about 48" down, then about 60" across to where it went up, and then back up about another 48", this is where the water would come out of the wall. We will have a shower sliding bar. Everything in copper.

The mixing valve is a Kohler 8304. When turning off the shower fast we get a hammer/knock, but it is not in the hot/cold supply lines. You can see it shake and feel it knock in the line that feeds the shower head. it seems most pronounced at the shower head end.

Any suggestions on how i can resolve this?

 

[breplum]

I have been involved with this kind of issue in many instances. The water hammer occurs as a normal part of hydraulic physics when water is stopped quickly, it is the reason the UPC calls for WHA (water hammer arrestors) on all fast-acting valves such as dishwashers and washing machine lines.
It is especially common when using volume control valves after thermostatic shower mixers.
Even with over-done pipe strapping and isolators, water hammer will occur.
You can try adding WHA to the hot and cold lines at the valve if the wall is still open or just the shower line. This assumes you still have access.

I have added water hammer arrestors with mixed results.
Redoing with PEX can help A LOT in this situation.